Two RCBS moulds, same alloy, same time...

[Typecaster]

A few months ago I smelted a 100-lb batch of WWs and immediately knew I'd done a VERY BAD THING. Despite all my sorting and fondling, something extra was in the melt—it seemed as if there was a less dense "layer" on top. Stirring the pot made the surface seem to shimmer and move at a different speed than the denser alloy. I cast ingots but kept them segregated to see if the metal was usable (since we never throw anything out, right?). Today was time for the test...

I usually cast with one mould at a time, but this morning I alternated between my trusty RCBS 357-150 KT and a new-to-me RCBS 45-250 KT. Ladle cast of the same alloy (1:4 mix of lino:WW mystery metal). I didn't use the thermometer, but by alternating moulds I know they were cast at the same temp.

After fluxing and skimming, the surface of the melt doesn't stay "clean and bright" for over 10 seconds before the thinner layer seems to show up. It seemed to cast perfectly in the .357 mould—perfectly filled out, absolutely no "frosting." But the .45 boolets are definitely frosted and didn't fill out well at all. Huh?

Why would one mould drop nice, shiny boolets and the other act like it was waaaay hot? As I said, I usually just use one mould at a time so I don't know if this is the norm. I do have an inquiring mind, though...

At least I found out that the contaminated mix is usable, even if I have to cast it all for the .357.

Richard

[leftiye]

Are ya ladle or bottom pouring? Two different molds should be driven to two different temps by the same temp alloy. The larger boolits impart more heat to the blocks - provided that the blocks are the same size, the heavier boolits would cast hotter.

I had some very contaminated alloy that would cast well IF you got it hot enough. It came to me cast in block letters! would have been a nightmare to ladle cast with. As the "oatmeal" floated, it might have cast okay from a bottom pour. I skimmed it all off, and tossed it.

[Typecaster]

These are all ladle-poured; my Lee lil-dripper bit the dust. The RCBS blocks are the same size, other than boolit weight.

[BABore]

If your thinking zinc contamination, doesn't it affect surface tension. Smaller boolit, less surface, different tension.

[garandsrus]

Typecaster,

If you are casting 35's and 44's, try two 35 casts for each 44 due to the different boolit size.

John

[AZ-Stew]

Given the same size mould blocks (both RCB$), the larger boolit will impart more heat to the mould (more molten alloy mass) and the mould block will have less mass to absorb it. Since the blocks are the same size, they have the same surface area from which to radiate the heat that's been put into them from the molten alloy. Therefore, the large caliber mould will heat faster and cool slower. Given the same rate of production (boolits per minute), the large caliber blocks will raise to a higher temperature than the smaller caliber mould. This is why you're getting frosted boolits from the .45 mould and nice shiny ones from the .38 mould.

Reduce casting temp or slow casting rate with the .45 mould and you should get the results you want.

Regards,

Stew

[runfiverun]

i'm with stew here
and the stuff you are seeing is just oxidized mix caused by your ladle going in and out of the pot.
your 45 boolits on the left are near the temp range and the ones on the right
are way too hot if you look in your mold you will see the effects[ coloration ]

[Typecaster]

Okay, the consensus is that I was working too quickly for the .45 mould. I can see that, as I'd fill the .45, swap moulds and cut the sprue of the .357, drop boolets, fill the .357, then swap moulds and cut the sprue on the .45...so I guess I was going a lot faster than usual.

As I said, I usually just use one mould at a time and develop a cadence for that one. I do like John's suggestion of casting 2 loads in the smaller mould to each of the larger. Once I find the rhythm, it should be a lot more productive than playing cast-and-wait with one mould.

Thanks for the input, all.

Richard

[Buckshot]

...............Yup, heat. In your photo the 2 slugs on the left look pretty good but it appears that the base band is a mite frosty on each. You have the sprue puddle sitting up there being big, fat and hot :-)

..................Buckshot

[Lloyd Smale]

stews got it. Alot of people love frosted bullets when they cast but i like mine slightly shinny. I just found to many times especially with high tin content alloys that frosting means not filling out totaly. Sometimes its hard to notice with the eye but it does happen.

[Larry Gibson]

I concur also, it's the heat. When working two moulds that same way and one is smaller I always cast 2 for 1 as previously suggested. Works for me.

Larry Gibson

[Typecaster]

Morning update: success! I gotz da rhythm!

Actually, I rotated between the 150-gr., 250-gr., and a 201-gr. SWC (so I can justify buying a 1911) for about an hour, and ended up with a pleasing pile of keepers. Zero frosting with the .357 or 201-gr.; and light base band frosting on the 250-gr. Keith at the end of the hour. Alloy temp: 700ºF.

I'll let these normalize for a month, then mike 'em...and that will determine the fate of my contaminated alloy.

Thanks again, gang.

Richard

[runfiverun]

i would run em out back and shootthem....

[Dennis Eugene]

Well I got to say I like your taste in molds and boolit style. Dennis